Polymeric composition

ABSTRACT

A composition comprising a polymer selected from a polyolefin, a polyamide or mixtures thereof, in admixture with an acrylic polymer additive, wherein: the extensional viscosity of the composition is greater than the extensional viscosity of the same composition not containing the acrylic polymer additive; or, the shear viscosity of the composition is greater than the shear viscosity of the same composition not containing the acrylic polymer additive; or, both the extensional viscosity and the shear viscosity of the composition is greater than the extensional viscosity and shear viscosity, respectively, of the same composition not containing the acrylic polymer additive, when measured at an identical applied specific shear rate in the range of 3000 S −1  to 500 S −1  under substantially the same conditions.

The present invention relates to a polymeric composition, a process for producing a polymeric composition, an article formed from the polymeric composition and the use of an acrylic polymer additive for modifying the melt rheology of a polymer. In particular, although not exclusively, the invention relates to a polyolefin and/or a polyamide having a modified melt-rheology, and the use of such modified polymers for forming an article.

Polyolefins, such as polyethylene, and polyamides, such as nylons, have been widely used in various industries for example the packaging industry to form articles such as containers or films, the automobile industry, or the textile industry to form fibres. Suitably, polyolefins and polyamides have been utilised in thermoforming processes, extrusion processes, moulding processes, for example extrusion blow-moulding and injection moulding, and fibre forming processes.

Although polyolefins and polyamides and polymeric mixtures including these polymers may possess desirable characteristics of melt-processability, such that the molten polymer has the desired melt-rheology to permit it to flow readily enough to be extruded, thermoformed, moulded or spun into a fibre, a particular problem associated with processing such polymers or polymeric mixtures is that the viscosity of the polymer or polymeric mixtures, respectively, may decline rapidly after the melt temperature is surpassed. This may lead to a rapid decline in the melt strength of the polymer or polymer mixture, respectively, which may produce production defects in the ultimate end product i.e. moulded article or fibre. For example, articles formed by a moulding process may include surface distortions and/or fractures therein e.g. holes, whereas strands of the polymer/polymeric mixture may break during extrusion or fibre-spinning.

Suitably, the overall effect resulting from a decline in melt viscosity of such a polymer/polymeric mixture after the melt temperature is surpassed may be a decrease in the overall efficiency of the ultimate product producing process.

The present invention therefore seeks to solve the aforementioned rheological problems associated with melt-processing a polyolefin or a polyamide.

According to a first aspect, the present invention provides a composition comprising a polymer selected from a polyolefin, a polyamide or mixtures thereof, in admixture with an acrylic polymer additive, wherein:

-   the extensional viscosity of the composition is greater than the     extensional viscosity of the same composition not containing the     acrylic polymer additive; or, -   the shear viscosity of the composition is greater than the shear     viscosity of the same composition not containing the acrylic polymer     additive; or, -   both the extensional viscosity and the shear viscosity of the     composition is greater than the extensional viscosity and shear     viscosity, respectively, of the same composition not containing the     acrylic polymer additive, -   when measured at an identical applied specific shear rate in the     range of 3000 s⁻¹ to 500 s⁻¹ under substantially the same     conditions.

By the term “same composition not containing the acrylic polymer additive” we mean a substantially identical composition of the present invention not containing the acrylic polymer additive.

According to a preferred embodiment of the present invention there is provided a composition comprising a polymer selected from a polyolefin, a polyamide or mixture thereof, in admixture with an acrylic polymer additive, wherein the extensional viscosity of the composition is greater than the extensional viscosity of the same composition not containing the acrylic polymer additive when measured at an identical applied specific shear rate in the range of 3000 s⁻¹ to 500 s⁻¹, preferably an identical applied specific shear rate in the range of 3000 s⁻¹ to 1000 s⁻¹, under substantially the same conditions.

Preferably, the extensional viscosity of the composition of the present invention is greater than the extensional viscosity of the polymer alone (i.e. polyamide or polyolefin or mixtures thereof) in the absence of the acrylic polymer additive when measured at an identical applied specific shear rate in the range of 3000 s⁻¹ to 500 s⁻¹, preferably at an identical applied specific shear rate in the range of 3000 s⁻¹ to 1000 s⁻¹, under substantially the same conditions.

According to an alternative embodiment of the present invention there is provided a composition comprising a polymer selected from a polyolefin, a polyamide or mixtures thereof, in admixture with an acrylic polymer additive, wherein the shear viscosity of the composition is greater than the shear viscosity of the same composition not containing the acrylic polymer additive when measured at an identical applied specific shear rate in the range of 3000 s⁻¹ to 500 s⁻¹, preferably at an identical specific shear rate in the range of 1000 s⁻¹ to 500 s⁻¹, under substantially the same conditions. Such a composition is also referred to hereinafter as the composition of the present invention.

Preferably, the shear viscosity of the composition of the present invention is greater than the shear viscosity of the polymer alone (i.e. polyamide or polyolefin or mixtures thereof) in the absence of the acrylic polymer additive when measured at an identical applied specific shear rate in the range of 3000 s⁻¹ to 500 s⁻¹, preferably at an identical specific shear rate in the range of 1000 s⁻¹ to 500 s⁻¹, under substantially the same conditions.

The composition according to the present invention may exhibit an increased extensional viscosity, and/or an increased shear viscosity, during melt processing in comparison with the same composition not containing the acrylic polymer additive. Conveniently, the use of the acrylic polymer additive (melt rheology modifier) may permit greater freedom and improved processing conditions for polyolefins and/or polyamides.

Suitably, the melt viscosity of the composition of the present invention may be increased, while the other positive melt-processable characteristics of polyamides and/or polyolefins, such as thermostability, may be substantially similar to those of the same composition, particularly the polymer alone, not containing the acrylic polymer additive. Consequently, the melt strength of the composition of the present invention may be higher than an identical composition, particularly the polymer alone, not including the acrylic polymer additive at a specific melt-processing temperature e.g. 170° C. to 300° C. Conveniently, the molten composition of the present invention may have the desired rheology to permit it to flow readily enough to be extruded, thermoformed, moulded or spun into a fibre, and it may have the desired melt strength to inhibit or prevent production defects e.g. distortion and/or fractures in the ultimate end product.

Conveniently, the overall effect resulting from an increase in the extensional viscosity, and/or an increase in the shear viscosity, of the composition of the present invention may be an increase in the efficiency and productivity of a fibre forming, film forming, extrusion, thermoforming or moulding process.

Furthermore, the composition of the present invention may be thermoplastically processed under conditions similar to those used for the same composition not containing the acrylic polymer additive, thereby negating the need to modify equipment for processing the composition of the present invention. Conveniently, the acrylic polymer additive may be inexpensive to produce.

By the term “extensional viscosity” we include the ability of a molten polymer per se or molten polymeric mixture (i.e. the molten composition of the present invention) to be drawn or pulled apart i.e. a non-rotational flow. In other words, a molten polymer or molten polymeric composition having a higher extensional viscosity requires increased force to extend the polymer or polymeric composition, respectively, over a unit length than a molten polymer or molten polymeric composition having a lower extensional viscosity.

By the term “shear viscosity” we include the internal resistance to flow, such as the ratio of shearing stress to the rate of shear, exhibited by a molten polymer per se or molten polymeric mixture (i.e. the molten composition of the present invention). In other words, a molten polymer or molten polymeric composition having a higher shear viscosity requires more force per unit area to cause two parallel polymer surfaces of unite area and unit distance apart to move past each other at unit velocity compared to a molten polymer and molten polymeric composition, respectively, having a lower shear viscosity i.e. shear viscosity relates to rotational flow.

As mentioned herein, increasing the extensional viscosity, and/or increasing the shear viscosity, of a molten polymer per se or a molten polymeric mixture may produce an increase in the melt strength of the polymer per se and polymeric mixture, respectively. Consequently, the efficiency of a process, such as extrusion, thermoforming, moulding or film forming, which is dependent to a certain extent on the melt strength of the polymer per se and polymeric mixture (i.e. the extent of production defects in articles formed from such processes), may be increased by increasing the melt strength of the polymer per se and polymeric mixture, provided that other factors such as the thermal stability of the polymer/polymeric mixture, are not significantly effected, as is typically the case with the composition of the present invention.

It will be appreciated by those skilled in the art that the extensional viscosity and shear viscosity of a molten polymer per se or molten polymeric mixture may depend on various factors, such as the temperature of the molten polymer or molten polymeric mixture, respectively, and the shear rate applied to the molten polymer or molten polymeric mixture. Consequently, in order to make comparisons between extensional viscosities and shear viscosities of molten polymers and/or molten polymeric mixtures it is typically necessary to apply a substantially identical specific shear rate to each of the molten polymers and/or molten polymeric mixtures, wherein the molten polymers and/or molten polymeric mixtures are at substantially identical temperatures. This is what we mean by “substantially the same conditions”.

Moreover, the extensional viscosity and shear viscosity of a molten polymer or molten polymeric mixture at a specific applied shear rate may depend on whether the specific applied shear rate is attained by increasing or decreasing the shear rate applied to the polymer or polymeric mixture.

Preferably, the specific identical shear rate applied to the molten polymer and/or molten polymeric mixtures is attained in the same manner (i.e. by decreasing or increasing the applied shear rate).

Accordingly, by the term “when measured at an applied identical shear rate in the range of 3000 s⁻¹ to 500 s⁻¹ under substantially the same conditions” in relation to extensional viscosity and shear viscosity, respectively, we mean the extensional viscosity or shear viscosity of the molten composition of the present invention, of the same molten composition of the present invention not containing the acrylic polymer additive and of the molten polymer alone in the absence of the acrylic polymer additive, respectively, when an identical specific shear rate of less than or equal to 3000 s⁻¹ and greater than or equal to 500 s⁻¹ is applied to each of the compositions and polymer alone, respectively, and the temperature of each of the molten compositions and molten polymer alone is substantially identical. Preferably, the identical specific shear rate applied to each of the molten compositions or molten polymer alone, respectively, is attained in the same manner.

Similarly, by the term “when measured at an applied identical shear rate in the range of 1000 s⁻¹ to 500 s⁻¹ under substantially the same conditions” in relation to shear viscosity we mean the shear viscosity of the molten composition of the present invention, of the same molten composition of the present invention not containing the acrylic polymer additive and of the molten polymer alone in the absence of the acrylic polymer additive, respectively, when an identical specific shear rate of less than or equal to 1000 s⁻¹ and greater than or equal to 500 s⁻¹ is applied to each of the compositions and polymer alone, respectively, and the temperature of each of the molten compositions and molten polymer alone is substantially identical. Preferably, the identical specific shear rate applied to the molten compositions or molten polymer alone, respectively, is attained in the same manner.

Suitably, when performing comparative measurements of extensional viscosity or shear viscosity, respectively, of the composition of the present invention, the polymer alone in the absence of the acrylic polymer additive, and the same composition of the present invention not containing the acrylic polymer additive, respectively, then these may be measured at substantially identical melt temperatures in the processing range of the polymer itself. The processing range of a given polymer may be regarded as the range between the minimum temperature at which individual particles of the polymer are fused together when subjected to heat or to a combination of heat and work on the polymer matrix, such that the polymer may be processed i.e. the polymer is molten, before degradation of the polymer has an unacceptable effect on the properties of the polymer.

Preferably, when performing comparative measurements of extensional viscosity or shear viscosity, respectively, the melt temperature of the polymer alone in the absence of acrylic polymer additive, the composition of the present invention and the same composition of the present invention not containing the acrylic polymer additive, is less than or equal to 330° C., more preferably less than or equal to 320° C., even more preferably less than or equal to 310° C. Preferably, when performing comparative measurements of extensional viscosity or shear viscosity, respectively, melt temperature of the polymer alone, the composition of the present invention and the same composition of the present invention not containing the acrylic polymer additive, is greater than or equal to 170° C., more preferably greater than or equal to 190° C., preferably greater than or equal to 200° C., even more preferably greater than or equal to 220° C., preferably greater than or equal to 250° C., more preferably greater than or equal to 270° C. i.e. at or above the operating temperature of the process at which the polymeric composition of the present invention and polymer alone is molten. It will however be appreciated that the extensional viscosity or shear viscosity, respectively, may be measured at lower temperatures, such as 190° C. to 210° C., provided that the material in question, such as the polymer alone and the composition of the present invention, is molten at such a temperature.

Most preferably, the extensional viscosity or shear viscosity, respectively, of the polymer alone in the absence of the acrylic polymer additive, the composition of the present invention, and the same composition of the present invention not containing the acrylic polymer additive is measured at a substantially identical temperature in the range of 280° C. to 320° C., preferably greater than or equal to 290° C., especially 290° C., when the polymer includes a polyamide as defined herein.

Most preferably, the extensional viscosity or shear viscosity, respectively, of the polymer alone, the composition of the present invention, and the same composition of the present invention not containing the acrylic polymer additive is measured at substantially the same temperature in the range of 170° C. to 250° C., when the polymer includes a polyolefin as defined herein, most preferably greater than or equal to 190° C., especially 190° C., when the polyolefin comprises polyethylene and most preferably greater than or equal to 230° C., especially 230° C., when the polyolefin comprises polypropylene.

Preferably, the identical specific shear rate applied to the composition of the present invention, to the polymer alone in the absence of the acrylic polymer additive, and the same composition of the present invention not containing the acrylic polymer additive, respectively may be obtained by reducing the shear rate applied to each molten composition and molten polymer alone, respectively, from a higher value to a lower value. In other words, when measuring the extensional viscosity or shear viscosity of the composition of the present invention and the polymer alone in the absence of the acrylic polymer, at an applied specific shear rate of, for example, 1000 s⁻¹, then this may be obtained by initially applying a higher shear rate to both the composition of the present invention and polymer alone, for example 1500 s⁻¹, and then reducing the shear rate to the desired applied specific shear rate i.e. from 1500 s⁻¹ to 1000 s⁻¹.

Typically, when performing comparative measurements of the shear viscosity and extensional viscosity of the composition of the present invention, the polymer alone in the absence of the acrylic polymer additive and the same composition of the present invention not containing the acrylic polymer additive, then these may be performed by applying a higher initial shear rate of 10,000 s⁻¹ to each of the molten compositions and the molten polymer alone, respectively, and then reducing the higher initial shear rate in stepwise fashion to 5000 s⁻¹, then to 3000 s⁻¹, then to 1500 s⁻¹, then to 1000 s⁻¹ and then to 500 s⁻¹, until the desired applied specific shear rate is attained. Suitably, the shear viscosity of a molten polymer or polymeric composition of the present invention is measured at a shear rate of greater than or equal to 50 s⁻¹, preferably greater than or equal to 100 s⁻¹, most preferably greater than or equal to 150 to 500 s⁻¹. Suitably, the shear viscosity of a molten polymer or molten polymeric composition of the present invention is measured at a shear rate of less than or equal to 10,000 s⁻¹, preferably less than or equal to 5000 to 3000 s⁻¹.

Preferably, when performing comparable measurements of extensional viscosity then a specific identical shear rate of 1500 s⁻¹ or 1000 s⁻¹ is applied to the composition of the present invention, the same composition of the present is invention not containing the acrylic polymer additive and the polymer alone, respectively. Most preferably a specific identical shear rate of 1000 s⁻¹ is applied to each of said compositions and the polymer alone respectively.

Preferably, when performing comparable measurements of shear viscosity then a specific identical shear rate of 1000 s⁻¹ or 500 s⁻¹, more preferably 1000 s⁻¹, is applied to the composition of the present invention, the same composition of the present invention not containing the acrylic polymer additive and the polymer alone, respectively.

Suitably, the composition of the present invention may have an extensional viscosity of greater than or equal to. 105%, preferably greater than or equal to 110%, more preferably greater than or equal to 115%, even more preferably greater than or equal to 120%, most preferably greater than or equal to 125% of the extensional viscosity of the same composition not containing the acrylic polymer additive, particularly of the polymer alone in the absence of the acrylic polymer additive.

Suitably, the composition of the present invention may have an extensional viscosity of less than or equal to 195%, preferably less than or equal to 190%, more preferably less than or equal to 185%, even more preferably less than or equal to 180% of the extensional viscosity of the same composition not containing the acrylic polymer additive, particularly of the polymer alone in the absence of the acrylic polymer additive.

Suitably, the composition of the present invention may have a shear viscosity that is greater than or equal to 105%, preferably greater than or equal to 110%, more preferably greater than or equal to 115%, most preferably greater than or equal to 120% of the shear viscosity of the same composition not containing the acrylic polymer additive, particularly of the polymer alone in the absence of the acrylic polymer additive.

Suitably, the composition of the present invention may have a shear viscosity that is less than or equal to 150%, preferably less than or equal to 145%, more preferably less than or equal to 140%, even more preferably less than or equal to 135%, most preferably less than or equal to 130% of the shear viscosity of the same composition not containing the acrylic polymer additive, particularly of the polymer alone in the absence of the acrylic polymer additive.

Preferably, when the composition of the present invention comprises a polyamide as defined herein, the composition of the present invention may have an extensional viscosity of greater than or equal to 110%, more preferably greater than or equal to 115%, even more preferably greater than or equal to 120%, even more preferably greater than or equal to 130%, most preferably greater than or equal to 135% of the extensional viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyamide polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyamide polymer, particularly 290° C.

Preferably, when the composition of the present invention comprises a polyamide as defined herein, the composition of the present invention may have an extensional viscosity of less than or equal to 185%, more preferably less than or equal to 180%, even more preferably less than or equal to 175%, most preferably less than or equal to 170% of the extensional viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyamide polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyamide polymer, particularly 290° C.

Preferably, when the composition of the present invention comprises a polyolefin as defined herein, the composition of the present invention may have an extensional viscosity of greater than or equal to 110%, more preferably greater than or equal to 115%, even more preferably greater than or equal to 120%, even more preferably greater than or equal to 130%, most preferably greater than or equal to 135% of the extensional viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyolefin polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyolefin polymer, particularly 190° C. to 230° C., especially at 190° C. when the polyolefin comprises polyethylene and at 230° C. when the polyolefin comprises polypropylene.

Preferably, when the composition of the present invention comprises a polyolefin as defined herein, the composition of the present invention may have an extensional viscosity of less than or equal to 195%, more preferably less than or equal to 190%, most preferably less than or equal to 187% of the extensional viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyolefin polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyolefin polymer, particularly 190° C. to 230° C., especially at 190° C. when the polyolefin comprises polyethylene and at 230° C. when the polyolefin comprises polypropylene.

Preferably, when the composition of the present invention comprises a polyamide as defined herein, the composition of the present invention may have a shear viscosity of greater than or equal to 105%, more preferably greater than or equal to 110%, even more preferably greater than or equal to 115%, most preferably greater than or equal to 120% of the shear viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyamide polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyamide polymer, particularly 290° C.

Preferably, when the composition of the present invention comprises a polyamide as defined herein, the composition of the present invention may have a shear viscosity of less than or equal to 150%, more preferably less than or equal to 140%, even more preferably less than or equal to 135%, most preferably less than or equal to 130% of the shear viscosity of the same composition of the present invention not containing the acrylic polymer additive, particularly the polyamide polymer alone, when measured at an applied specific shear rate of 1000 s⁻¹ at the melt-processing temperature of the polyamide polymer, particularly 290° C.

Preferably, when performing comparative measurements of extensional viscosity or shear viscosity, respectively, of the composition of the present invention, the polymer alone in the absence of the acrylic polymer additive and the same composition of the present invention not containing the acrylic polymer additive, sufficient time is allowed to elapse after reducing the shear rate to the desired applied specific shear rate, so that each of the compositions and polymer alone, respectively, have equilibrated at the desired identical applied specific shear rate.

Suitably, each of the compositions and polymer alone, respectively, may be allowed to equilibrate for less than or equal to 400 s, preferably less than or equal to 200 s, preferably less than or equal to 150 s, preferably less than or equal to 100 s, more preferably less than or equal to 75 s after reducing the shear rate from a higher value to the desired identical applied specific shear rate.

Suitably, each of the compositions and the polymer alone, respectively, may be allowed to equilibrate for greater than or equal to 5 s, preferably greater than or equal to 10 s, preferably greater than or equal to 20 s, preferably greater than or equal to 30 s, more preferably greater than or equal to 50 s after reducing the shear rate from a higher value to the desired identical applied specific shear rate.

Preferably, when performing comparative measurements of the extensional viscosity then these may be performed at an extensional stress of greater than or equal to 100 KPa, preferably greater than or equal to 120 KPa, more preferably greater than or equal to 150 KPa, even more preferably greater than or equal to 160 KPa, even more preferably greater than or equal to 180 KPa.

Preferably, when performing comparative measurements of extensional viscosity then these may be performed at an extensional stress of less than or equal to 900 KPa, preferably less than or equal to 800 KPa, more preferably less than 700 KPa, even more preferably less than or equal to 600 KPa, even more preferably less than or equal to 500 KPa, even more preferably less than or equal to 400 KPa, most preferably less than or equal to 300 KPa.

Suitably, comparative measurements of the extensional viscosity of the composition of the present invention, the polymer alone, or the same composition of the present invention not containing the acrylic polymer additive may be measured at approximately the same extensional stress as defined above i.e. the extensional stress of the composition of the present invention may be within ±35%, preferably ±25%, more preferably ±20% of the extensional stress of the polymer alone.

Preferably, the physical form of the composition of the present invention, or the same composition of the present invention not containing the acrylic polymer additive, and polymer alone in the absence of the acrylic polymer additive should be substantially identical to each other. Preferably, the composition of the present invention, or the same composition of the present invention not containing the acrylic polymer additive, and the polymer alone in the absence of the acrylic polymer additive comprise a cylindrical pellet, preferably the cylindrical pellet has a cross-sectional diameter of greater than or equal to 0.1 mm and less than or equal to 3 mm, and a length of less than or equal to 3 mm. A cylindrical pellet having a length of 3 mm and a cross-sectional diameter of 3 mm is especially preferred.

Preferably, substantially all the moisture is removed from the composition of the present invention, the same composition of the present invention not containing the acrylic polymer additive, and the polymer alone in the absence of the acrylic polymer additive before measuring extensional and/or shear viscosities. Preferably, each of the compositions and the polymer alone is dried under vacuum, preferably at a temperature of 170° C., preferably from greater than or equal to 6 hours and less than or equal to 24 hours.

Preferably, when performing comparative measurements of extensional viscosity or shear viscosity, respectively, then these may be measured at substantially the same pressures.

Preferably, the maximum pressure exerted on the polymer alone in the absence of the acrylic polymer additive, the composition of the present invention, and the same composition of the present invention not containing the acrylic polymer additive is less than or equal to 30 Mpa, preferably less than or equal to 25 Mpa, preferably less than or equal to 20 Mpa, more preferably less than or equal to 15 Mpa.

Preferably, the maximum pressure exerted on the polymer alone in the absence of the acrylic polymer additive, the composition of the present invention and the same composition of the present invention not containing the acrylic polymer additive is greater than or equal to 0.5 Mpa, preferably greater than or equal to 1 Mpa, preferably greater than or equal to 3 Mpa, more preferably greater than or equal to 5 Mpa.

Suitably, it will be appreciated by persons skilled in the art that variables which may substantially effect extensional viscosity and shear viscosity measurements should preferably be substantially identical when performing comparative measurements.

All shear viscosity and extensional viscosity measurements may be obtained using a Rosand Capillary rheometer by methods well known to those skilled in the art as described herein.

It will be appreciated that the compositions of the present invention may exhibit both an increase in shear viscosity and an increase in extensional viscosity, particularly within the values as defined herein, compared to the polymer alone in the absence of the acrylic polymer additive and the composition of the present invention not containing the acrylic polymer additive, when measured under substantially the same conditions as defined herein. Such compositions are also embraced by the scope of the present invention.

Preferably, the acrylic polymer additive is not a multi-stage polymer, particularly a multi-stage particulate polymer such as a core-shell polymer comprising a core polymer that is surrounded by or linked to a separate shell polymer e.g. an impact modifier particle. Suitably, the acrylic polymer additive is a linear or branched polymer. Preferably, the acrylic polymer additive is a linear polymer. Preferably, the acrylic polymer additive is thermoplastically processable.

Suitably, the acrylic polymer additive is amorphous. Preferably, the acrylic polymer additive is substantially immiscible with the polymer (e.g. polyolefin or polyamide). By the term “substantially immiscible” we include that at the melt-processing temperatures when the composition of the present invention is molten, for example typically 190 to 310° C., the acrylic polymer additive forms a two-phase melt with the polymer. Microscopic examination of such a melt shows a two-phase system in which the immiscible molten acrylic polymer is usually in the form of spherical particles or globules dispersed in a continuous molten polymer matrix.

Suitably, the composition of the present invention may be molten or in solid form, such as in the form of pellets, sheets, granules or powder. The pellets may be thermally processed for any downstream application. Preferably, when the composition of the present invention is in solid or molten form the polymer (i.e. polyolefin or polyamide) forms a polymer matrix with the acrylic polymer additive dispersed therein.

Suitably, the acrylic polymer additive in the composition of the present invention may, particularly in the ultimate end product i.e. shaped article, film or fibre, have a maximum cross-sectional dimension of less than or equal to 400 nm, more preferably less than or equal to 300 nm. Suitably, the acrylic polymer additive in the composition of the present invention, particularly in the ultimate end product i.e. shaped article, film or fibre, may have a maximum cross-sectional dimension of greater than or equal to 50 nm, more preferably greater than or equal to 75 nm. A particularly preferred maximum cross-sectional dimension of the acrylic polymer additive in the composition of the present invention, particularly in the ultimate end product, is 200 nm.

The size of the acrylic polymer additive in the composition of the present invention, such as its cross-sectional dimension, may be measured by techniques well known to those skilled in the art, for example, by scanning or transmission electron microscopy. In scanning electron microscopy, the composition of the present invention is frozen, typically in liquid nitrogen, and then fractured to expose the additive material whose size is measured by an electron microscope. In transmission electron microscopy, the composition of the present invention is frozen, typically in liquid nitrogen, and then pieces are shaved off for analysis with an electron microscope.

Preferably, the acrylic polymer additive does not include a liquid crystal polymer i.e. it does not form an anisotropic melt in the temperature range at which the thermoplastic polymeric mixture is melt-processed e.g. at a temperature of 190° C. to 330° C. as defined herein, after a shear stress is removed.

Preferably, the acrylic polymer additive includes less then 2% by weight of a styrene polymer. More preferably, the acrylic polymer additive includes less than 1% by weight, most preferably less than 0.5% by weight, of a styrene polymer. Especially preferred acrylic polymer additives do not include any styrene polymer.

The acrylic polymer additive suitably includes homopolymers and copolymers (which term includes polymers having more than two different repeat units), comprising monomers of acrylic acid and/or alkacrylic acid and/or alkyl(alk)acrylate. As used herein, the term “alkyl (alk)acrylate” refers to either the corresponding acrylate or alkacrylate ester, which are usually formed from the corresponding acrylic or alkacrylic acids. In other words, the term “alkyl (alk)acrylate” refers to either an alkyl alkacrylate or an alkyl acrylate.

Preferably, the alkyl (alk)acrylate is a (C₁-C₂₂)alkyl ((C₁-C₁₀)alk)acrylate. Examples of C₁-C₂₂ alkyl groups of the alkyl (alk)acrylates include methyl, ethyl, n-propyl, n-butyl, iso-butyl, tert-butyl, iso-propyl, pentyl, hexyl, cyclohexyl, 2-ethyl hexyl, heptyl, octyl, nonyl, decyl, isodecyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, behenyl, and isomers thereof. The alkyl group may be straight or branched chain. Preferably, the (C₁-C₂₂)alkyl group represents a (C₁-C₆)alkyl group as defined above, more preferably a (C₁-C₄)alkyl group as defined above. Examples of C₁₋₁₀ alk groups of the alkyl (alk)acrylate include methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, pentyl, hexyl, cyclohexyl, 2-ethyl hexyl, heptyl, octyl, nonyl, decyl and isomers thereof. The alk groups may be straight or branched chain. Preferably, the (C₁-C₁₀)alk group represents a (C₁-C₆)alk group as defined above, more preferably a (C₁-C₄) alk group as defined above.

Preferably, the alkyl (alk)acrylate is a (C₁-C₄)alkyl. ((C₁-C₄) alk)acrylate, most preferably a (C₁-C₄)alkyl (meth)acrylate. It will be appreciated that the term (C₁-C₄) alkyl (meth)acrylate refers to either (C₁-C₄)alkyl acrylate or (C₁-C₄)alkyl methacrylate. Examples of (C₁-C₄)alkyl (meth)acrylate include methyl methacrylate (MMA), ethyl methacrylate (EMA), n-propyl methacrylate (PMA), isopropyl methacrylate (IPMA), n-butyl methacrylate (BMA), isobutyl methacrylate (IBMA), tert-butyl methacrylate (TBMA), methyl acrylate (MA), ethyl acrylate (EA), n-propyl acrylate (PA); n-butyl acrylate (BA), isopropyl acrylate (IPA), isobutyl acrylate (IBA), tert-butyl acrylate (TBA), and combinations thereof.

Preferably, the alkacrylic acid monomer is a (C₁-C₁₀)alkacrylic acid. Examples of (C₁-C₁₀)alkacrylic acids include methacrylic acid, ethacrylic acid, n-propacrylic acid, iso-propacrylic acid, n-butacrylic acid, iso-butacrylic acid, tert-butacrylic acid, pentacrylic acid, hexacrylic acid, heptacrylic acid and isomers thereof. Preferably the (C₁-C₁₀)alkacrylic acid is a (C₁-C₄)alkacrylic acid, most preferably methacrylic acid.

Preferably, the acrylic polymer is an acrylic copolymer. Preferably, the acrylic copolymer comprises monomers derived from alkyl (alk)acrylate, and/or acrylic acid and/or alkacrylic acid as defined herein. Most preferably, the acrylic copolymer comprises monomers derived from alkyl (alk)acrylate, i.e. copolymerisable alkyl acrylate monomers and alkyl alkacrylate comonomers as defined herein. Especially preferred acrylic copolymers include a (C₁-C₄)alkyl acrylate monomer and a copolymerisable (C₁-C₄)alkyl (C₃-C₄)alkacrylate comonomer as defined herein. Most preferred acrylic copolymers are formed from a methyl methacrylate monomer and a copolymerisable (C₁-C₄)alkyl acrylate comonomer, particularly methyl acrylate and/or ethyl acrylate and/or butyl acrylate, especially ethyl acrylate or n-butyl acrylate.

Preferably, the acrylic copolymer comprises greater than or equal to 0.1% by weight, preferably greater than or equal to 0.5% by weight, more preferably greater than or equal to 1% by weight, even more preferably greater than or equal to 3% by weight of an alkyl acrylate monomer as defined herein based on the total weight of the acrylic copolymer. Preferably, the acrylic copolymer comprises less than or equal to 20%, preferably less than or equal to 17%, more preferably less than or equal to 15% by weight of an alkyl acrylate monomer as defined herein based on the total weight of the acrylic copolymer.

Preferably, the acrylic copolymer comprises less than or equal to 99.9% by weight, preferably less than or equal to 99.5% by weight, more preferably less than or equal to 99% by weight, even more preferably less than or equal to 97% by weight of a copolymerisable alkyl alkacrylate comonomer as defined herein, particularly methyl methacrylate, based on the total weight of the acrylic copolymer. Preferably, the acrylic copolymer comprises greater than or equal to 80%, preferably greater than or equal to 83%, more preferably greater than or equal to 85% by weight of a copolymerisable alkyl alkacrylate comonomer as defined herein, particularly methyl methacrylate, based on the total weight of the acrylic copolymer.

Preferably, the acrylic polymer comprises greater than or equal to 80 wt %, more preferably greater than or equal to 85 wt %, more preferably greater than or equal to 90 wt %, more preferably greater than or equal to 95 wt %, especially greater than or equal to 96 wt % methyl methacrylate based on the total weight of the acrylic polymer.

Preferably, the alkyl acrylate is a (C₁-C₄)alkyl acrylate, as defined herein. Most preferably, the alkyl acrylate is ethyl acrylate and/or butyl acrylate and isomers thereof.

Preferably, the acrylic copolymer comprises a homopolymer or copolymer derived from a monomer mixture comprising 80 to 100 wt % of methyl methacrylate, 0 to 20 wt % of at least one other copolymerisable alkyl (alk)acrylate comonomer, 0 to 0.5 wt % of an initiator, and 0 to 1.0 wt % of a chain transfer agent.

Preferably, where the acrylic polymer is an acrylic copolymer, particularly an acrylic copolymer including methyl methacrylate, the acrylic polymer comprises a single copolymerisable alkyl acrylate as defined herein, preferably a (C₁-C₄) alkyl acrylate, especially ethyl acrylate or butyl acrylate and isomers thereof.

Preferably, the acrylic copolymer comprises 0.1 to 20% by weight of an alkyl acrylate monomer, particularly a (C₁-C₄) alkyl acrylate monomer, as defined herein and 80 to 99% by weight of a copolymerisable alkyl alkacrylate comonomer, particularly methyl methacrylate, as defined herein. More preferably, the acrylic copolymer comprises 1 to 15% by weight of an alkyl acrylate monomer, particularly a (C₁-C₄) alkyl acrylate monomer, and 85 to 99% by weight of copolymerisable methyl methacrylate comonomer. Especially preferred acrylic copolymers comprise 3 to 15% by weight of an alkyl acrylate monomer, particularly a (C₁-C₄) alkyl acrylate monomer, as defined herein, particularly ethyl acrylate or butyl acrylate, and 97 to 85% by weight of copolymerisable methyl methacrylate comonomer.

Highly preferred acrylic copolymers include 3%, 10% and 15% by weight of an alkyl acrylate monomer, particularly ethyl acrylate or n-butyl acrylate, based on the total weight of the acrylic copolymer, and 97%, 90% and 85% by weight respectively of methyl methacrylate comonomer based on the total weight of the acrylic copolymer.

Suitably, where the acrylic polymer is a copolymer derived from a monomer mixture of at least one alkyl alkacrylate monomer as defined herein, particularly methyl methacrylate, and at least one other copolymerisable alkyl acrylate comonomer as defined herein, particularly ethyl and/or butyl acrylate, the ratio of the weight of alkyl alkacrylate to the weight of alkyl acrylate in the acrylic copolymer is suitably greater than or equal to 4:1, preferably greater than or equal to 5:1, preferably is greater than or equal to 6:1, preferably greater than or equal to 8:1, preferably greater than or equal to 10:1, more preferably greater than or equal to 15:1, more preferably greater than or equal to 19:1.

Unexpectedly, it has been found that if the molecular weight of the acrylic polymer additive as defined herein is below a threshold value then the composition of the present invention may exhibit the desired increase in extensional viscosity and/or shear viscosity.

Preferably, the acrylic polymer has a weight average molecular weight greater than 50,000, more preferably greater than 75,000, most preferably greater than 80,000. Preferably the acrylic polymer has a weight average molecular weight less than 300,000, preferably less than 200,000, most preferably less than 150,000. An acrylic polymer having a weight average molecular weight in the range of approximately 85,000 to 150,000 is especially preferred. Suitably, the weight average molecular weight of the acrylic polymer may be measured by techniques well known to those skilled in the art, such as gel permeation chromatography.

The acrylic polymer may be synthesised by techniques well known to those skilled in the art, such as suspension polymerisation as outlined in Kirk-Othmer Encyclopaedia of Chemical Technology, John Wiley and Sons. Vol. 16 p. 506-537, particularly p. 525-727. Suitably, the suspension polymerisation method involves the polymerisation of one or more monomers of acrylic acid, alkacrylic acid or alkyl (alk)acrylate as defined herein in the presence of one or more initiators and one or more chain transfer agents.

Suitable initiators include free radical initiators such as peroxy, hydroperoxy and azo initiators, for example, 2,2′-azo-bis(isobutyronitrile) (AIBN), 2,2′-azo-bis(2,4-dimethylvaleronitrile), azo-bis(α-methylbutyronitrile), acetyl peroxide, dodecyl peroxide, benzoyl peroxide. Preferably, the acrylic polymer includes at least 0.01 wt %, more preferably at least 0.02 wt %, most preferably at least 0.04 wt % initiator based on the total weight of the acrylic polymer. Preferably, the acrylic polymer includes less than 0.5 wt %, more preferably less than 0.3 wt %, most preferably less than 0.25 wt % initiator based on the total weight of the acrylic polymer.

Suitable chain transfer agents include thiols, such as dodecyl mercaptan, n-propyl mercaptan, n-butyl mercaptan, t-butyl mercaptan, 2-ethyl hexyl, thioglycollate, thiophenol and butanthiol. Preferably, the acrylic polymer includes at least 0.03 wt %, preferably at least 0.05 wt %, preferably at least 0.8 wt %, preferably at least 0.1 wt %, most preferably at least 0.15 wt % chain transfer agent based on the total weight of the acrylic polymer. Preferably, the acrylic polymer includes less than 1 wt %, preferably less than 0.9 wt %, preferably less than 0.8 wt %, preferably less than 0.7 wt %, preferably less than 0.6 wt %, most preferably less than 0.5 wt % chain transfer agent based on the total weight of the acrylic polymer.

Preferably, the molar ratio of initiator to chain transfer agent employed in the polymerisation process is less than or equal to 11:1, preferably less than or equal to 8:1, preferably less than or equal to 7:1, more preferably less than or equal to 6:1, more preferably less than or equal to 5:1, most preferably less than or equal to 4:1.

Preferably, the molar ratio of chain transfer agent to initiator employed in the polymerisation process is preferably greater than or equal to 1:1, preferably greater than or equal to 1.5:1, more preferably greater than or equal to 2:1.

An especially preferred range of the molar ratio of chain transfer agent to initiator employed in the polymerisation process is greater than or equal to 1:1 and less than or equal to 2.5:1.

Suitably, the acrylic polymer may include the aforementioned molar ratios of initiator to change transfer agents.

Suitably, the polymer (e.g. the polymer matrix) of the composition of the present invention includes a polymer comprising a polyamide and/or polyolefin. Preferably, the polyamide is thermoplastically processable. Preferably, the polyolefin is thermoplastically processable. As mentioned previously, the polymer in the molten composition of the present invention typically forms a molten polymer matrix in which the acrylic polymer additive as defined herein is dispersed.

When a polyamide is used, the polyamide may include homopolymers or copolymers synthesised by polycondensation of an aliphatic or aromatic diamine such as hexamethylene diamine, nonamethylene diamine and m-xylene diamine with an aliphatic or aromatic dicarboxylic acid such as adipic acid, sebacic acid and terephthalic acid, or they may be synthesised from polymerisation of a lactam such as ε-caprolactam and ω-lauro lactam or from the self-polycondensation of amino acids such as ε-aminocaproic acid and 11-aminoundecanoic acid. Preferably the polyamide includes nylon-6,6 (polyhexamethylene adipimide), nylon-6 (poly-ε-caprolactam), nylon-11, nylon-6,10 (polyhexamethylene sebacamide) and copolymers thereof. The homopolymers are preferred. However, copolymers are also included within the scope of the present invention. When the polyamide comprises a copolymer then copolymers formed by copolymerising a polyamide monomer, such as nylon-6,6, with at least one other, preferably only one other, copolymerisable polyamide comonomer e.g. nylon-6, are preferred. Preferably, when the polyamide is a copolymer, the copolymer is formed by copolymerising a polyamide monomer with only a copolymerisable polyamide comonomer. Suitably, preferred copolymers do not include composite resins such as poly(amide-polyester) resins. For example, we include nylon-6,6/nylon-6 and nylon-6,6/nylon-6TA, where 6TA represents a hexamethylene terephthalamide unit. Among these polyamides homopolymers of nylon-6 and nylon-6,6 are especially preferred.

When a polyolefin is used, the polyolefin may be derived by polymerising at least one mono-alpha olefin monomer, preferably at least one mono-alkene monomer i.e. an alkene having a single double bond. Preferably, the at least one mono-alkene monomer comprises a C₂-C₈ alkene, especially a linear or branched (i.e. non-aromatic, cyclic or heterocyclic) C₂-C₈ alkene monomer, such as ethene, propene, but-1-ene, 2-methyl-propene (isobutene), pent-1-ene, pent-2-ene, 3-methyl-pent-1-ene, 2-methyl-but-1-ene, 4-methyl-pent-1-ene, 3-methyl-but-1-ene, 4-methyl-pent-2-ene, hex-1-ene, hex-2-ene and hex-3-ene. Preferred C₂-C₈ alkene monomers include ethene, propene, but-1-ene, 2-methyl-propene, 3-methyl-but-1-ene and 4-methyl-1-pent-1-ene. Especially preferred C₂-C₈ alkene monomers include ethene, propene and but-1-ene.

Preferred polyolefins are homopolymers derived from polymerising one mono-alkene monomer, particularly a C₂-C₈ alkene monomer, as defined herein. Preferred homopolymers include polyethylene, such as low-density polyethylene, high-density polyethylene and linear low-density polyethylene, polypropylene, and homopolymers derived from polymerising 2-methyl-propene monomers, 3-methyl-but-1-ene monomers and 4-methyl-pent-1-ene monomers. Especially preferred homopolymers include polyethylene and polypropylene.

Although less preferred, copolymers of polyolefins are also included within the scope of the present invention. Preferred copolymers are derived from copolymerising a mono-alkene monomer, particularly a linear or branched C₂-C₈ alkene monomer, as defined herein with at least one other, preferably only one, copolymerisable linear or branched C₂-C₈ alkene comonomer. Preferably, when the polyolefin is a copolymer, the copolymer is formed by copolymerising a polyolefin monomer with only a copolymerisable polyolefin comonomer. Suitably, preferred copolymers do not include composite resins such as poly(styrene-ethylene) polymers. Preferred copolymers include poly(ethylene-propylene), poly(propylene-but-1-ene) and poly(ethylene-oct-1-ene).

Preferred compositions of the present invention include: nylon and an acrylic polymer additive; polyethylene and an acrylic polymer additive; and, polypropylene and an acrylic polymer additive.

The polyamide or polyolefins may comprise one or more agents selected from a glass filler, mineral filler, flame retardant, UV stabiliser, delustering agent, a thermal stabilizer, an ultraviolet absorber, an antistatic agent, a terminating agent and a fluorescent whitening agent, or a mixture of two or more of these agents.

Preferably, the acrylic polymer additive is present in an amount of at least 0.1 wt %, more preferably at least 0.25 wt %, even more preferably at least 0.5 wt %, most preferably greater than or equal to 1 wt % based on the total weight of the composition of the present invention.

Preferably, the acrylic polymer additive is present in an amount of less than or equal to 20 wt %, preferably less than or equal to 15 wt %, more preferably less than or equal to 12 wt %, most preferably less than or equal to 5 wt % based on the total weight of the composition of the present invention.

The addition of such low amounts of acrylic polymer may further reduce the costs of the overall process, thereby allowing significant increases in productivity to be achieved. However, it will be appreciated that the acrylic polymer additive may be added to the polymer matrix in an amount of greater than 1.0 wt % of the polymer matrix if desired.

Preferably, the amount of polymer (i.e. polyolefin or polyamide) in the composition of the present invention is greater than or equal to 80 wt %, preferably greater than or equal to 85 wt %, more preferably greater than or equal to 88 wt %, most preferably greater than or equal to 95 wt % based on the total weight of the composition of the present invention.

Preferably, the amount of polymer (i.e. polyolefin or polyamide) in the composition of the present invention is less than or equal to 99.9 wt %, preferably less than or equal to 99.75 wt %, more preferably less than or equal to 99.5 wt %, most preferably greater than or equal to 99 wt % based on the total weight of the composition of the present invention.

Preferably, the amount of additive that is added to the polymer should be kept as low as possible to achieve the desired increase in extensional viscosity and/or shear viscosity whilst maintaining the physical properties i.e. thermal stability, substantially similar to that of the unmodified polymer.

It will be appreciated by those skilled in the art, as exemplified by the specific non-limiting examples as described hereinafter, that the amount of increase in the extensional viscosity and/or the shear viscosity of the composition of the present invention compared with the same composition not containing the acrylic polymer additive, particularly the polymer alone, may be dependent, amongst other things, on the amount of acrylic polymer additive added, average molecular weight of the acrylic polymer additive, and the type of acrylic polymer additive. Consequently, by routine experimentation it is usually possible to produce a composition of the present invention having the desired increase in extensional viscosity and/or shear viscosity for the particular application e.g. extrusion moulding, injection moulding or blow moulding whilst maintaining the physical properties of the composition of the present invention substantially similar to that of the same composition, particularly the polymer alone, in the absence of the additive.

The acrylic polymer additive may be incorporated into a polymer as defined herein by various methods. For example, the addition of the additive may be effected during the polymerisation process for forming the polymer. Alternatively, the additive may be melt-blended with the polymer. For example, the acrylic polymer additive may be compounded with the polymer to form a pellet which is subsequently extruded and processed for example moulded into an article. Furthermore, the additive may be mixed with the polymer in the hopper of an extruder and the resultant mixture extruded and processed. Alternatively, a melt stream of the additive may be added to a melt stream of the polymer, by a side extrusion or injection process. Preferably, the acrylic polymer additive is melt-blended with the polymer employing the above methods at a temperature between 150° C. to 300° C. preferably 170° C. to 290° C., more preferably 160° C. to 240° C. when the polymer comprises a polyolefin and 260° C. to 290° C. when the polymer comprises a polyamide.

Most preferably, non-molten acrylic polymer additive is added to a melt stream of the polymer by a cramming process. By adding non-molten acrylic polymer additive to such a melt stream, enables the polymeric composition of the present invention to be easily controlled and/or varied during the production process. The adaptability of the production equipment may result in significant cost savings and enhanced productivity, particularly if it is necessary to vary the polymeric composition of the present invention. Moreover, this type of addition process may minimise the exposure of the acrylic polymer additive to the high temperature polymer processing conditions, thereby forming a more stable polymer mixture.

According to a second aspect, the present invention provides a method of making a composition of the present invention as defined herein comprising providing a polymer selected from a polyamide and/or polyolefin as defined herein, and adding an acrylic polymer additive as defined herein to the polymer. It will be appreciated that any of the aforementioned methods of adding the additive to the polymer may be employed. Preferably, the acrylic polymer additive is melt-blended with the polymer. Preferably, non-molten acrylic polymer additive is added to the molten polymer.

According to a third aspect, the present invention provides a use of the composition of the present invention to form a fibre. Preferably, the process for producing a polymeric fibre comprises providing a molten composition of the present invention as defined herein, and forming a fibre from the molten composition of the present invention.

Preferably, the molten composition of the present invention is formed by adding non-molten acrylic polymer additive to the molten polymer.

Preferably, the production of the polymeric fibre is accomplished by high speed spinning using spinning devices which are known per se. Preferably, spinning speeds of greater than or equal to 500 m/minute, more preferably greater than or equal to 2000 m/minute, most preferably 3000 m/minute are employed. Preferably, the spinning speed is less than or equal to 10000 m/minute, more preferably less than or equal to 7500 m/minute, most preferably less than or equal to 6000 m/minute.

According to a fourth aspect the present invention provides a fibre comprising the composition of the present invention.

The composition of the present invention may be made in the form of sheets, film, powders or granules. It may be extruded or moulded into various shapes or coextruded or laminated onto other materials, rigid or foamed forms of ABS, PVC, polystyrene polymers including high impact polystyrene (HIPS). It may also be coextruded or laminated onto metals. When the composition of the present invention is in the form of sheets it may be thermoformed into a desired shape.

According to a fifth aspect, the present invention provides a shaped article comprising the composition of the present invention. Suitably, said shaped article may be formed by extrusion, by moulding such as blow-moulding or injection-moulding, thermoforming or coextruded or laminated onto other materials.

Said shaped article may be for use in construction of a building. For example, it could be a solid or coextruded building component, for example a soffit board, barge board, fascia board, cladding board, siding, gutter, pipe, shutters, window casement, window board, window profile, conservatory profile, door panels, door casement, roofing panel, architectural accessory or the like.

Said shaped article may be for use in constructing a vehicle or in another automotive application, both as a bulk material or as a coextruded laminate. Such applications, include but are not limited to, decorative exterior trim, cab mouldings, bumpers (fenders), louvers, rear panels, accessories for buses, trucks, vans, campers, farm vehicles and mass transit vehicles, side and quarter panel trim or the like.

Said shaped article may be used in applications both indoors or outdoors, for example bathroom fixtures, toilet seat, kitchen housewares, bottles, containers, refrigerator liners or bodies, fencing, trash cans, garden furniture or the like.

According to a sixth aspect, the present invention provides a use of the composition of the present invention to form a shaped article.

According to a seventh aspect, the present invention provides a film comprising the composition of the present invention. Suitably, the film may be formed by blow-moulding or extruding the composition of the present invention. Typically, the film has a thickness of 10 microns to 2 mm.

According to an eighth aspect, the present invention provides a use of the composition of the present invention to form a film.

According to a ninth aspect the present invention provides the use of an acrylic polymer additive as defined herein for increasing the extensional viscosity and/or the shear viscosity of a polymer, particularly a polyamide or polyolefin, as defined herein. Suitably, such use may be affected by admixing the acrylic polymer additive as defined herein with a polyamide or polyolefin by the methods described herein.

Suitably, features of the first, second, third, fourth, fifth, sixth, seventh, eighth and ninth aspects of the present invention may be combined and regarded as preferred features of the other aspects of the present invention.

The invention will be further described by way of the following non-limiting examples with reference to the accompanying drawings, wherein:

Rheological Analysis

Viscosity measurements were made using a Rosand Capillary rheometer at a temperature of between 190° C. to 310° C. Shear viscosity measurements were made at shear rates of between 30 s⁻¹ and 10,000 s⁻¹, and elongational extensional viscosities calculated from these data as outlined below. The thermal stability of the composition and the additives was assessed by monitoring the viscosity over 1800 s.

In the capillary rheometry analysis, the polymer chip (i.e. the polymer composition or the additive) is heated to the desired temperature (i.e. melted) and simultaneously extruded through two barrels: one barrel containing an elongated die (16 mm in length) and 1 mm in diameter; and, the other barrel containing an orifice die (0.2 mm in length) and 1 mm in diameter. Pressure transducers are located upstream of each of the respective die entry regions to record the pressure drop through each die for an individual shear rate i.e. ram speed. Two parallel measurements are made to allow for die entry correction to be made. For both dies (i.e. elongated and orifice die) a contribution to the total pressure drop recorded is attributed to the resistance of the polymer melt converging in the die entry region (which is analogous to stretching a unit cell of molten polymer i.e. extensional viscosity). A further contribution to the pressure drop occurs with the elongated die but not the orifice die, which is attributable to the resistance to flow of the polymer melt due to shear with the die walls.

Consequently, the pressure drop recorded through the orifice die relates to the extensional viscosity of the polymer melt, as no shear occurs at the die walls unlike in the elongated die having die walls. Similarly, the difference in the pressure drop between the elongated die and the orifice type die produces a measure of the shear viscosity of the polymer melt.

The deformation and flow of a polymer system is generally carried out in shear for measurement convenience and related as shear viscosity (η), shear rate (γ) or shear stress (T). The elongational viscosity (λ) is then calculated by the software in the rheometer in accordance with Cogswell's equation: $\lambda = {\frac{9}{32}\left( \frac{n + 1}{\eta} \right)^{2}\left( \frac{p_{o}}{\gamma} \right)^{2}}$ where η represents shear viscosity, n represents the shear thinning exponent, γ represents shear strain and P_(o) represents the extrapolated zero length die pressure drop.

EXAMPLE 1

Preparation of an acrylic copolymer additive comprising 98.25% by weight methyl methacrylate and 1.75% by weight ethyl ethylacrylate by suspension polymerisation.

A 5 litre round bottom flask with four baffles in the flask walls and equipped with a shaft driven paddle stirrer passing down an alembic condenser is charged with 28 g disodium hydrogen phosphate dihydrate, 2000 g deionised water, and 100 g of 1% sodium polymethacrylate (high molecular weight polymethylacrylate, neutralised with NaOH) solution in water. The suspension is heated to 40° C. to 50° C. with stirring to dissolve the sodium polymethacrylate, and nitrogen is bubbled through the solution for 30 minutes to remove oxygen. The nitrogen purge is stopped and 1080 g methyl methacrylate, 19.25 g ethyl acrylate, 2.50 g 2,2′-azobis(isobutyronitrile) (AIBN) and 3.40 g dodecyl mercaptan are then charged to the reaction flask. A nitrogen blanket is maintained over the reactants. The reaction mixture is heated to the reaction temperature of 82° C. and maintained while the reaction proceeds. The stirrer speed may need to be increased during the reaction exotherm which can push the temperature up to ca. 95° C. and water may need to be added if the batch foams excessively. After the exotherm begins to subside the bath is heat-treated to reduce residual monomer levels and decompose any residual initiator by heating at 90° C. for 1 hour. The reaction mixture is cooled and then centrifugally washed by pouring the reaction slurry into a centrifuge bag, dewatering and washing with 2×2 litres deionised water, with dewatering between each addition. The centrifuge bags have a pore size of ca. 75 microns. The filtered and washed polymer is spread onto trays and dried in an air oven at a temperature of 75° C. for 24 hours, to yield the title acrylic copolymer having a weight average molecular weight of 98,000 measured by gel permeation chromatography.

The acrylic copolymer had a melt flow index MFI (ASTM D1238, 230° C., 3.8 kg) of 2.3 g/10 minutes.

EXAMPLE 2

Preparation of an acrylic copolymer additive comprising 99.5% by weight methyl methacrylate and 0.5% by weight ethyl acrylate by bag polymerisation.

The following materials were thoroughly mixed in a 10 litre glass round bottomed flask using a shaft driven paddle stirrer passing down an alembic condenser:

-   4923.30 g methyl methacrylate -   24.70 g ethyl acrylate -   2.40 g lauryl peroxide -   0.54 g t-butyl peroxyacetate (50% active) -   23.09 g dodecyl mercaptan -   0.73 g oxalic acid solution (7.16% w/w in water) -   0.91 g 75% w/w sodium dioctyl sulphosuccinate in ethanol/water (AOT     75) -   4.95 g dithio-bis-stearylpropionate -   19.80 g stearyl methacrylate

The reaction mixture is stirred and the flask purged with nitrogen for 30 minutes. The monomer mixtures produced are charged into a nylon 6,6(or nylon 6) polymer bag having a wall thickness less than 0.8 mm for polymerisation. The bag is similar in appearance to a plastic trash bag with dimensions sufficient to accommodate the monomer mixture and yield a bag thickness of no more than 3 cm. The bag is placed on a metal tray and filled with the monomer mixture. Trapped air is removed and the bag sealed with a metal clip. The tray and bag are placed in a suitably designed oven and the oven temperature controlled as detailed in the table below: Step Temperature Time 1 63° C. 1.5 h 2 58° C. 13.5 hr 3 62° C. 1 h 4 65° C. 2 h 5 75° C. 1 h 6 100° C.  1 h 7 130° C.  2 h

This profile achieved a conversion level of >98% and produced a bulk polymer of very smooth appearance with no irregularities or “hot spots” at the surface. The nylon bag was removed to yield the title acrylic copolymer having a weight average molecular weight of 77,000.

EXAMPLE 3

Preparation of an acrylic copolymer additive comprising 85% by weight methyl methacrylate and 15% by weight n-butyl acrylate by suspension polymerisation.

The title acrylic copolymer additive is prepared by the experimental methodology as outlined in Example 1 employing the following reactants:

-   30.8 g disodium hydrogen phosphate dihydrate -   2200 g deionised water -   110 g 1% sodium polymethacrylate (high molecular weight     polymethylacrylate, neutralised with NaOH) in water -   765 g methyl methacrylate -   135 g n-butyl acrylate -   2.0 g 2,2′-azobis(isobutyronitrile) AIBN -   3.0 g dodecyl mercaptan

The title acrylic copolymer additive was found to have a weight average molecular weight of 85,000 by gel permeation chromatography.

EXAMPLE 4

Preparation of an acrylic copolymer additive comprising 90% by weight methyl methacrylate and 10% by weight n-butyl acrylate by suspension polymerisation.

The title copolymer additive is prepared by the experimental methodology as outlined in Example 1 employing the following reactants.

-   28.0 g disodium hydrogen phosphate dihydrate -   2000 g deionised water -   100 g 1% sodium polymethacrylate (high molecular weight     polymethylacrylate, neutralised with NaOH) in water -   990 g methyl methacrylate -   110 g n-butyl acrylate -   2.5 g 2,2′-azobis(isobutyronitrile) AIBN -   3.5 g dodecyl mercaptan

The title acrylic copolymer additive was found to have a weight average molecular weight of 86,000 by gel permeation chromatography.

EXAMPLE 5

Preparation of an acrylic copolymer additive comprising 97% by weight methyl methacrylate and 3% by weight ethyl acrylate by suspension polymerization.

The title acrylic copolymer additive is prepared by the experimental methodology as outlined in Example 1 employing the following reactants.

-   28.0 g disodium hydrogen phosphate dihydrate -   2000 g deionised water -   100 g 1% sodium polymethacrylate (high molecular weight     polymethylacrylate, neutralised with NaOH) in water -   1067 g methyl methacrylate -   33 g ethyl acrylate -   2.5 g 2,2′-azobis(isobutyronitrile) AIBN -   2.0 g dodecyl mercaptan

The title acrylate copolymer additive was found to have a weight average molecular weight of 136,000 by gel permeation chromatography.

EXAMPLE 6

General Procedure for Preparing a Composition of the Present Invention

A mixture comprising the desired pelletised polymer (e.g. polyamide or polyolefin) and a pelletised acrylic polymer additive is fed to a twin screw extruder, such as a ZSK30 twin screw extruder by Werner Pfleiderer, running at 270° C. when the polymer comprises polyamide and running at 190° C. when the polymer comprises polyethylene, with a screw speed of 275 revolutions per minute and an output from the extruder of 15 kg/hour. The composition of the present invention exiting the extruder is cooled in a water bath prior to pelletisation using a rotary hall/cutter unit.

Using the above procedure the following compositions were prepared:

-   Composition 1: 99% by weight polyamide-6,6 (extrusion grade Zytel     E50 available from DuPont). 1% by weight acrylic copolymer additive     of Example 3 comprising 85% by weight methyl methacrylate and 15% by     weight n-butyl acrylate (referred to as 15% nBA). -   Composition 2: 99% by weight polyamide-6,6 (extrusion grade Zytel     E50 available from DuPont). 1% by weight acrylic copolymer additive     of Example 5 comprising 97% by weight methyl methacrylate and 3% by     weight ethyl acrylate (referred as 3% EA) -   Composition 3: 99% by weight polyethylene [of melt flow index 9     (190° C., 2.16 kg, g/10 minutes) ISO 1133] and density 920 kgm⁻³     (ISO 1183D, ISO 1872-2B). -    1% by weight acrylic copolymer additive of Example 4 comprising 90%     by weight methyl methacrylate and 10% by weight n-butyl acrylate     (referred as 10% nBA).

EXAMPLE 7 Rheological Measurements of Compositions 1 and 2

The shear viscosities and extensional viscosities of: (1) polyamide-6,6 (extrusion grade Zytel E50 available from DuPont) in the absence of an acrylic copolymer additive; (2) composition 1 as outlined in Example 6; and (3) composition 2 as outlined in Example 6 were determined at 290° C.

In all experiments the shear viscosity and the extensional viscosity of the polymeric compositions and polyamide-6,6 were measured at an initial shear rate of 10,000 s⁻¹. Further measurements of extensional viscosity and shear viscosity were made at the specified shear rates by decreasing the shear rate from 10000 s⁻¹ to 6000 s⁻¹, then to 3000 s⁻¹, then to 1500 s⁻¹, then to 1000 s⁻¹, then to 500 s⁻¹, then to 300 s⁻¹, then to 100 s⁻¹, then to 60 s⁻¹, and finally to 30 s⁻¹.

The results are tabulated in Table 1 and demonstrate that the polymeric compositions of the present invention exhibits increased extensional and increased shear viscosity compared with the polymer alone in the absence of the acrylic polymer additive. Typically, this may lead to an overall increase in the productivity of a moulding, coextrusion, thermoforming or film forming process.

EXAMPLE 8 Rheological Measurements of Composition 3

The shear viscosities and extensional viscosities of: (1) polyethylene [of melt flow index 9 (190° C., 2.16 kg, g/10 minutes) ISO 1133 and density 920 kgm⁻³ (ISO 1183D, ISO 1872-2B)] alone; and (2) composition 3 as outlined in Example 6 were-determined at 190° C.

The extensional viscosity of the polymeric composition and polyethylene was measured at an initial shear rate of 10,000 s⁻¹. Further measurements of extensional viscosity and shear viscosity were made at the specified shear rates by decreasing the shear rate from 10000 s⁻¹ to 6000 s⁻¹, then to 3000 s⁻¹, then to 1500 s⁻¹, then to 1000 s⁻¹, then to 500 s⁻¹, then to 300 s⁻¹, then to 100 s⁻¹, then to 60 s⁻¹, and finally to 30 s⁻¹.

The results are tabulated in Table 2 and demonstrate that the polymeric composition of the present invention exhibits increased extensional viscosity compared with the polymer alone in the absence of the acrylic polymer additive. Typically, this may lead to an overall increase in the productivity of a moulding, coextrusion, thermoforming or film forming process. TABLE 1 Shear viscosity and extensional viscosity results measured at 290° C. for polyamide- 6,6 alone, composition 1 of the present invention (polyamide-6,6 plus 1% by wt of an acrylic polymer additive 15% BA), and composition 2 of the present invention (polyamide-6,6 plus 1% by weight of an acrylic polymer additive 3% EA). Shear Polyamide-6,6 alone Composition 1 Composition 2 rate Shear Extensional Shear Extensional Shear Extensional per viscosity Extensional Viscosity viscosity Extensional Viscosity viscosity Extensional Viscosity second Pa · s stress KPa KPa · s Pa · s stress KPa KPa · s Pa · s stress KPa KPa · s 30 257 387.6 384.4 50 273.2 408.4 26.2 1.35 374.4 100 256.2 36.1 1.02 363.6 55.4 1.69 350.5 150 245.2 51.1 0.95 335.7 67.7 1.21 323.4 300 222.4 93.4 0.87 280.2 142.5 1.61 277 138 1.53 500 194 162.7 1.09 240.5 219.2 1.6 241.6 214.4 1.52 1000 152.3 265 0.92 189.4 375.6 1.49 185.4 348.6 1.31 1500 132.8 379.8 0.97 155.9 506 1.46 135.2 462.8 1.23 3000 99.7 647.2 0.93 110.2 813.7 1.54 108.5 743.1 1.13 5000 76.6 1036.7 1.12 83.4 1187.8 1.55 79.87 1049.6 1.1

TABLE 2 Extensional viscosity results measured at 190° C. for polyethylene and composition 3 of the present invention (polyethylene plus 1% by weight of an acrylic polymer additive 10% nBA). Polyethylene alone Composition 3 Shear Shear Exten- Extensional Exten- Extensional rate per viscosity sional Viscosity sional Viscosity second Pa · s stress KPa KPa · s stress KPa KPa · s 30 171.4 50 177.9 100 185.2 150 208.2 64 1.75 300 171.6 105.8 1.45 144.2 2.95 500 136.1 158 1.47 217 3.19 1000 105.3 249.5 1.18 324.8 2.18 1500 88.2 326.6 1.08 424.1 1.89 3000 64.9 515.9 0.91 646.8 1.44 5000 50.3 689.6 0.76 854.6 1.17 10000 33.5 1013.1 0.61 1233.7 0.91

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 

1-34. (canceled)
 35. A composition comprising a polymer selected from a polyamide, a polyolefin or mixtures thereof, in admixture with an acrylic polymer additive having a weight average molecular weight of less than 300,000 and comprising a homopolymer or copolymer derived from a monomer mixture comprising 80 to 100 wt % of methyl methacrylate, 0 to 20 wt % of at least one other copolymerizable alkyl (alk)acrylate comonomer, 0 to 0.5 wt % of an initiator, 0 to 0.1 wt % of a chain transfer agent, wherein: the extensional viscosity of the composting is greater than the extensional viscosity of the same composition not containing the acrylic polymer additive; or, the shear viscosity of the composition is greater than the shear viscosity of the same composition not containing the acrylic polymer additive; or, both the extensional viscosity and the shear viscosity of the composition are greater than the extensional viscosity and shear viscosity, respectively, of the same composition not containing the acrylic polymer additive, when measured at an identical applied specific shear rate in the range of 3000 s⁻¹ to 500 s⁻¹ under substantially the same conditions.
 36. A composition as claimed in claim 35 wherein the acrylic polymer additive comprises a homopolymer or copolymer derived essentially from a monomer mixture comprising 80 to 100 wt % of methyl methacrylate, 0 to 20 wt % of at least one other copolymerizable alkyl (alk)acrylate comonomer, 0 to 0.5 wt % of an initiator and 0 to 0.1 wt % of a chain transfer agent.
 37. A composition as claimed in claim 35 wherein the acrylic polymer additive is an acrylic copolymer derived from a monomer mixture comprising 80 to 99.9% by weight of methyl methacrylate and 0.1 to 20% by weight of at least one other copolymerizable alkyl (alk)acrylate.
 38. A composition as claimed in claim 37 wherein the alkyl (alk) acrylate comprises an alkyl acrylate.
 39. A composition as claimed in claim 38 wherein the alkyl acrylate comprises a (C₁-C₄) alkyl acrylate.
 40. A composition as claimed in claim 37 wherein the acrylic copolymer comprises a single copolymerizable alkyl acrylate comonomer.
 41. A composition as claimed in claim 35 wherein the acrylic polymer additive has a weight average molecular weight of greater than or equal to 50,000.
 42. A composition as claimed in claim 35 wherein the acrylic polymer additive is present in an amount of at least 0.5 wt % based on the total weight of the composition.
 43. A composition as claimed in claim 35 wherein the acrylic polymer additive is present in an amount of less than or equal to 15 wt % based on the total weight of the composition.
 44. A composition as claimed in claim 35 wherein the polymer is present in an amount of greater than or equal to 80 wt % based on the total weight of the composition.
 45. A composition as claimed in claim 35 wherein the acrylic polymer additive is immiscible with the polymer.
 46. A composition as claimed in claim 35 wherein the composition is molten.
 47. A composition as claimed in claim 35 wherein the polyamide comprises a nylon.
 48. A composition as claimed in claim 47 wherein the nylon comprises nylon-6, 6 or nylon-6.
 49. A composition as claimed in claim 35 wherein the polyolefin comprises a homopolymer or copolymer derived from a monomer mixture comprising a mono-alkene monomer and at least one other copolymerizable mono-alkene comonomer.
 50. A composition as claimed in claim 49 wherein the polyolefin comprises polyethylene or polypropylene.
 51. A composition as claimed in claim 35 wherein the polymer is a homopolymer.
 52. A composition as claimed in claim 35 wherein the acrylic polymer additive has a weight average molecular weight in the range of 85,000 to 150,000.
 53. A composition as claimed in claim 35 wherein the extensional viscosity of the composition is greater than or equal to 105% of the extensional viscosity of the same composition not containing the acrylic polymer additive.
 54. A composition as claimed in claim 35 wherein the shear viscosity of the composition is greater than or equal to 105% of the shear viscosity of the same composition not containing the acrylic polymer additive.
 55. A composition as claimed in claim 35 wherein comparative measurements of shear viscosity or extensional viscosity of the composition and the same composition not containing the acrylic polymer additive are performed at a substantially identical melt temperature.
 56. A composition as claimed in claim 35 wherein the extensional viscosity of the composition is greater than or equal to 105% of the extensional viscosity of the polymer alone.
 57. A process for preparing a composition as defined in claim 35 comprising adding an acrylic polymer additive as defined in claim 35 to a polymer selected from a polyamide, a polyolefin or mixtures thereof.
 58. A process as claimed in claim 57 wherein the acrylic polymer additive is melt-blended with the polymer.
 59. A process as claimed in claim 57 wherein non-molten acrylic polymer additive is added to a melt of the polymer.
 60. A fiber comprising the composition as defined in claim
 35. 61. A shaped article comprising the composition as defined in claim
 35. 62. A method for increasing the extensional viscosity, the shear viscosity, or a combination thereof of a polymer selected from a polyamide, a polyolefin, or mixtures thereof as claimed in claim 35, the method comprising admixing an acrylic additive as claimed in claim 35 with the polymer. 